This invention relates to a projector system for supplying a light beam capable of forming a ring-shaped image on a plane, and also to a system for detecting a flaw in an annular portion of an object, using such a projector system.
A projector system, disclosed in Japanese Laid-Open (Kokai) Patent Application No. 80220/88 (corresponding to U.S. patent application Ser. No. 100,523 now abandoned), includes a cylindrical fiber conduit (optical converter element) comprising a number of parallel optical fibers. When a light beam is caused to be incident upon the fiber conduit in a direction perpendicular to the axis of the fiber conduit, a light beam radiating in a plane perpendicular to the axis of the fiber conduit is emitted from the fiber conduit. This outgoing light beam appears as a linearly-extending image on a plane parallel to the axis of the fiber conduit.
The above Japanese Laid-Open Patent Application No. 80220/88 discloses another prior art projector system in which a cylindrical lens is used as an optical converter element.
U.S. Pat. No. 3,964,824 discloses a projector system similar to that described in the above Japanese Laid-Open Patent Application No. 80220/88.
Japanese Laid-Open Patent Application No. 133048/78 discloses a projector system which comprises a light source, and a pair of first and second cylindrical lenses. A light beam generated from the light source is incident on the first cylindrical lens in a direction perpendicular to the axis of the first cylindrical lens. As a result, the light beam, spreading out at a certain angle in a plane perpendicular to the axis of the first cylindrical lens, is emitted from the first cylindrical lens. This outgoing light beam is converged in the direction of the axis of the first cylindrical lens by the second cylindrical lens whose axis is inclined relative to the axis of the first cylindrical lens.
All of the above conventional projector systems are designed to supply the light beam which appears as a linear image on the plane.
In a projector system disclosed in Japanese Utility Model Publication No. 21073/79, a light beam, advancing along a thin band-like path, is caused to be incident on a cylindrical lens in a direction inclined relative to the axis of the cylindrical lens. As a result, the light beam emitted form the cylindrical lens spreads out along part of an imaginary conical surface, and forms an arc-shaped image in a certain plane; however, this image is not in the form of a complete or closed circle.